Several genes implicated in neurological disease are thought to regulate Rho GTPase signaling, yet there is a limited understanding of how these signaling proteins function. WRP (WAVE associated Rac GAP protein), which was identified by positional cloning as a gene disrupted in 3p-syndrome mental retardation (MR), is one such protein. WRP regulates actin remodeling by binding to the Rac effector WAVE-1 and by stimulating Rac GTP hydrolysis. WAVE-1 null mice exhibit dramatic behavioral impairments in learning and memory tests. Importantly, the phenotype of WAVE-1 null mice overlaps well with those of 3p-syndrome retardation, supporting a link between WRP regulated signaling and MR. The objective of this application is to examine the molecular mechanisms regulating WRP and whether loss of WRP affects specific neuronal functions that contribute to behavioral impairments. Our central hypothesis is that one cellular function of WRP is to regulate actin signaling in spines. Thus loss of WRP would lead to spine abnormalities and cognitive impairments. This hypothesis is guided by strong preliminary data based on 1) structure/function and imaging data defining a WRP targeting domain and 2) data linking WRP and WAVE-1 to spinogenesis, synaptic plasticity and cognitive behavior. The specific aims of this grant are: 1) Identify the mechanisms that spatially target and regulate WRP. We will use a combination of biochemical and imaging approaches designed to address how WRP is regulated and may be targeted to subcellular compartments. 2) Delineate the cellular role of anchored WRP. Because WRP regulates Rac and WAVE-1, we hypothesize targeting of WRP is a salient feature of this signaling pathway in spines. We will use imaging and cellular assays to quantify the role of WRP targeting in synapse function. 3) Test the in vivo function of WRP in regulating cognitive behavior and synapse function. Using a conditional WRP null mouse model we will analyze aspects of synapse function in vivo and in vitro. We will also examine these mice for abnormalities in a range of behaviors related to 3p-syndrome retardation. Because this proposal utilizes a multidisciplinary approach to analyze WRP signaling, a fundamental advance in understanding the mechanisms linking actin signaling to neuronal dysfunction can be anticipated. PUBLIC HEALTH RELEVANCE: This research is relevant to the mission of NIH because it examines the functional role of a gene implicated in mental retardation at the molecular, cellular and organismal level. Thus, important advances in understanding the etiology of mental retardation could be anticipated. It is also expected that knowledge gained in these studies will shed light on other forms of neuropathologies that involve abnormal Rho-GTPase signaling and mechanisms that normally regulate neuronal connectivity.